a) Field of the Invention
This invention relates to an ink-jet recording sheet, and especially to an ink-jet recording sheet having an ink-receiving layer which is excellent especially in the absorbency of a water-based ink, can provide stable printed characters, picture, pattern or the like (hereinafter collectively called "printed marks" for the sake of brevity) of high quality, and is also superb in transportability, blocking resistance, waterproofness and moisture resistance.
b) Description of the Related Art
Ink-jet recording is to perform recording of an image, characters or the like by causing tiny droplets of an ink to fly and stick on a recording sheet made of paper or the like. Various operation principles have been proposed including, for example, the electrostatic attraction method, the method that mechanical vibrations or displacements are applied to an ink by means of a piezoelectric element, and the method that an ink is heated to bubble and the resulting pressure is used. As a recording method which permits high-speed recording, produces less noise and enables high-quality printing and multicolor printing, ink-jet recording is finding ever-increasing utility for various applications.
For use in such ink-jet recording, various recording sheets have been proposed, including recording sheets provided on paper or like bases with ink-receiving layers, which are composed primarily of various pigments and resins, or recording sheets containing porous pigments incorporated in themselves upon making paper so that prompt absorption of ink and formation of well-defined ink dots can be assured without a reduction in print quality due to blotting and/or bleeding of the ink adhered on the recording sheets.
For example, JP Kokai No. 57-82085 discloses to provide an ink-receiving layer composed of a water-soluble polymer in combination with both an inorganic pigment and an organic pigment as pigments, and JP Kokai No. 62-268682 discloses to provide an ink-receiving layer composed of fine powdery silica and a polyvinyl alcohol copolymer containing silanol groups.
However, keeping the step with improvements in the performance of ink-jet recording machines, such as high-speed recording, high-density recording and full-color recording, and the resulting expansion of their application fields, it has also become necessary for ink-jet recording sheets to have high-level characteristics such as:
(1) Prompt ink absorption and large ink absorption capacity. PA1 (2) High color-producing ability for inks. PA1 (3) High surface strength on the ink-receiving layer. PA1 (4) High waterproofness of the base material so that the base material will not develop roughness or curling by an ink. PA1 (5) Good mark storability, such as waterproofness and ozone resistance, after printing of marks on the ink-receiving layer. PA1 (6) No quality changes of the ink-receiving layer along the passage of time. PA1 polyethylene glycol, PA1 copolymerized polyol of polyethylene glycol and polytetramethylene glycol, PA1 copolymerized polyol of polyethylene glycol and polypropylene glycol, PA1 polyethylene glycol adipate, PA1 polyethylene glycol succinate, PA1 copolymerized polyol of polyethylene glycol and poly-.epsilon.-caprolactone, and PA1 copolymerized polyol of polyethylene glycol and poly-.gamma.-valerolactone. PA1 polyethylene oxide diamine, PA1 polyethylene oxide propylene oxide diamine, PA1 polyethylene oxide triamine, and PA1 polyethylene oxide propylene oxide triamine. PA1 (1) The resin is emulsified in a form of o/w or w/o, and the resulting emulsion is coated on a base material sheet to form a film. PA1 (2) The resin is provided with a portion soluble in an organic solvent and a portion insoluble in said organic solvent. By making use of this solubility difference in the organic solvent, the resin is formulated into a dispersion, which is then coated on a base material sheet to form a film. PA1 (3) A solution of the resin in an organic solvent, which has compatibility with water, is coated on a base material sheet, and the base material sheet is then dipped in water to eliminate the solvent. PA1 (4) A dispersion of the resin, another resin and an additive is prepared. The dispersion is coated on a base material sheet to form a film. The another resin and additive are then selectively eliminated. PA1 (5) A film is formed from the resin with an inorganic filler dispersed therein. The film is then stretched into a porous sheet, which is then bonded to a base material sheet.
To meet these requirements, it has been proposed or studied to use a porous pigment or water-soluble polymer having excellent ink absorbency as a component of an ink-receiving layer to be placed on an ink-jet recording sheet, to use a latex for an improvement in the waterproofness of an ink-receiving layer, and to use as a base material itself a synthetic paper sheet, plastic sheet or the like equipped with waterproofness.
However, those making use of paper as a base material or a water-soluble polymer alone as an ink-receiving layer have poor waterproofness so that blotting takes place at printed parts and printed marks are hence inferior in definition. On the other hand, those making use of a synthetic paper sheet or plastic film as a base material and those making use of a latex as a resin in an ink-receiving layer involve problems in the adhesion between the ink-receiving layer and the base material and in ink absorbency and ink drying property.